#define  _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
// Definition for singly - linked list.
// struct ListNode {
//    int val;
//    struct ListNode* next;
//    
//};

typedef struct ListNode ListNode;
struct ListNode* reverseList(struct ListNode* head)
{
    if (head == NULL)
    {
        return NULL;
    }
    ListNode* n1, * n2, * n3;
    n1 = NULL;
    n2 = head;
    n3 = n2->next;

    while (n2)
    {
        n2->next = n1;
        n1 = n2;
        n2 = n3;
        if (n3)
        {
            n3 = n3->next;
        }



    }

    return n1;

}